German Patent Application No. DE 41 10 453 A1 describes a charger in which the voltage of the secondary battery to be charged is measured and used to control the charging current. This method serves to stop the charging process when the voltage of the secondary battery begins to drop from its peak value, which is interpreted as a sign of a sufficiently charged secondary battery.
Furthermore, European Patent Application No. EP 0 288 213 A1 describes a device for charging a battery, which device serves to control the charging current as a function of the state of charge or discharge of a battery. A control logic which is connected to a current sensor in order to detect the charging current serves this purpose. Usually, a shunt resistor is used for the current sensor, the signal which is tapped off at this resistor then being amplified by means of an operational amplifier.